The present invention relates to an air lock with tabs for closing ducts for the passage of air, smoke and the like.
Air locks of this type comprise a frame, a passage port defined by the frame and a plurality of side by side tabs supported in a rotating manner by the frame and extending through the passage port. In addition there are provided kinematic connection means between the tabs to ensure simultaneous and synchronised movement of each of said tabs between a closed position wherein all the tabs are essentially coplanar and close the passage port and an open position rotated by approximately 90.degree. in relation to the closed position.
The kinematic connection means can be provided by means of gear wheels integral in rotation with each tab and meshed directly with each other. In this manner each gear wheel rotates in the direction opposite that of the tabs adjacent thereto. As an alternative, there are employed kinematic rack or lever mechanisms of various types permitting optionally operation of all the tabs in the same rotation direction while keeping them parallel to one another.
In any case the kinematic connection means are brought together and supported on the same side of the frame, either towards the interior thereof (i.e. towards the passage port) or towards the exterior.
The choice between the two arrangements usually allows for different factors among which are the degree of environment severity, the possibility of perfect closing of the passage port, and ease of production and installation.
Indeed, an inward arrangement subjects the kinematic connection means to the flow traversing the air lock which could cause damage due to the deposit of dirt such as e.g. in a painting station or due to the corrosive effects of e.g. smoke exhaust. In addition, an inward arrangement makes perfect closing of the air lock practically impossible.
On the other hand even an outward arrangement is not free of shortcomings since even the external environment where the duct in which is inserted the air lock is located can be a source of problems due to the accumulation of dirt or even to the presence of corrosive substances. Furthermore, with an outward arrangement the utmost care must be taken to prevent foreign bodies from accidentally jamming or obstructing movement of the kinematic mechanism.
For these reasons a solution often adopted consists of positioning the kinematic connection means externally and protecting them with a special cover.